# Bubble game collision

1. Jun 28, 2013

### cloa513

Suppose a bubble with some small mass and constant velocity hits a bundle of "bubbles"- the collision is unusual- there is no dynamic friction but the point of contact sticks- they are springy so both compress by a third before returning to their former shape. The new total bundle can't translate but can rotate. What's the deceleration? so I can F=ma and take tangential component to calculate Ft and Torque so that T=Iw.

2. Jun 28, 2013

### Viracocha

you'd just have to use the momentum of the first bubble then it's a transfer of momentum for a collision. As long as they don't pop (and accounting for air resistance), the bubbles are pretty much just shells, which collide about the same as spheres

3. Jun 29, 2013

### cloa513

So should I take it as
Δω=m/M*(vt/ d)
Δω change in angular velocity
m mass of bubble
M of bubble
vt tangential velocity of colliding bubble
d distance from fixing point (which may or may not the centre of the bundle).

Its my computer game- I don't understand or trust the physics engine and I'd like it to be physically reasonable.

4. Jun 29, 2013

### Viracocha

That seems like it should work, you should also be able to use conservation of energy

5. Jun 29, 2013

### cloa513

Energy is not conserved for the system. It can't translate because either there is out of plane fixing device or it can induce powerful wind currents to keep it in position. A similar real world application could be a free rotating plate- its fixed to ground- it get hit with all sort of powerful particles (say its in the explosion zone of a mine) and you want to know will it spin too much and break itself. Another one is a harrier jet or helicopter hovering- how much rotation will it get if you effectively autocounteract the translation but not the rotation and will it be effective in certain conditions.